Bug 2060: Windows: no access to microphone causes crash

Problem:
1. Set no access to microphone in Privacy category of Settings app.
2. Try to record in a new track. (not append to an existing track.)
3. Audacity crashes.

Cause of crash:
TrackPanel::OnTrackListResizing is called with a track after a call to
TrackList::ClearPendingTracks, which has removed its owner.
TrackPanel::OnTrackListResizing ends up calling TrackPanel::UpdateTrackVRuler,
and this function calls TrackList::Channels(t)), which assumes the track has an owner.
Crash.

Fix: in TrackPanel::OnTrackListResizing, check that the track has an owner.

src/Track.h

@@ -329,6 +329,8 @@ public:
    // For use when loading a file.  Return true if ok, else make repair
    bool LinkConsistencyCheck();
 
+   bool HasOwner() const { return static_cast<bool>(GetOwner());}
+
 private:
    std::shared_ptr<TrackList> GetOwner() const { return mList.lock(); }
 

src/TrackPanel.cpp

@@ -715,7 +715,8 @@ void TrackPanel::OnTrackListResizing(TrackListEvent & e)
 {
    auto t = e.mpTrack.lock();
    // A deleted track can trigger the event.  In which case do nothing here.
-   if( t )
+   // A deleted track can have a valid pointer but no owner, bug 2060
+   if( t && t->HasOwner() )
       UpdateVRuler(t.get());
    e.Skip();
 }